…leware handlers (nicolas-grekas)This PR was merged into the 4.2-dev branch.Discussion----------[Messenger] make Envelope first class citizen for middleware handlers| Q             | A| ------------- | ---| Branch?       | 4.2| Bug fix?      | no| New feature?  | no| BC breaks?    | yes| Deprecations? | no| Tests pass?   | yes| Fixed tickets | -| License       | MIT| Doc PR        | -This PR sits on top of#28909 so that only the 2nd commit should be reviewed for now, until I rebase it.This idea has already been proposed and rejected in#27322.Yet, now that I've reviewed in depth the component, I politely but strongly suggest to reconsider.Middleware handlers are the central piece of the routing layer.When `dispatch()` accepts `object|Envelope`, it's because it sits on the outer boundary of the component. `handle()` on the contrary plugs inside its core routing logic, so that it's very legitimate to require them to deal with `Envelope` objects. Yes, some middleware care only about the message inside. That's fine calling `getMessage()` for them.Right now, we built a complex magic layer that acts as a band-aid *just* to save this call to `getMessage()`. For middleware that want the envelope, we require an additional interface that magically *changes* the expected argument. That's very fragile design: it breaks the `L` in `SOLID`...Looking at the diff stat, this is most natural.Commits-------ae46a43 [Messenger] make Envelope first class citizen for middleware handlers